The present invention relates generally to tape drives and, more particularly, to flanged tape guides having a wear resistant coating.
Information is recorded on and read from a moving magnetic tape with a magnetic read/write head positioned next to the tape. The magnetic xe2x80x9cheadxe2x80x9d may be a single head or, as is common, a series of read/write head elements stacked individually and/or in pairs within the head unit. Data is recorded in tracks on the tape by moving the tape lengthwise past the head. The head elements are selectively activated by electric currents representing the information to be recorded on the tape. The information is read from the tape by moving the tape longitudinally past the head elements so that magnetic flux patterns on the tape create electric signals in the head elements. These signals represent the information stored on the tape.
Data is recorded on and read from each of the parallel tracks on the tape by positioning the head elements at different locations across the tape. That is, head elements are moved from track to track as necessary to either record or read the desired information. Movement of the magnetic head is controlled by an actuator operatively coupled to some type of servo control circuitry. Tape drive head positioning actuators often include a lead screw driven by a stepper motor, a voice coil motor, or a combination of both. The carriage that supports the head is driven by the actuator along a path perpendicular to the direction that the tape travels. The head elements are positioned as close to the center of a track as possible based upon the servo information recorded on the tape.
FIG. 1 illustrates generally the configuration of a tape drive 10 typical of those used with single spool tape cartridges. Referring to FIG. 1, a magnetic tape 12 is wound on a single supply spool 14 in tape cartridge 16. Tape cartridge 16 is inserted into tape drive 10 for read and write operations. Tape 12 passes around a first tape guide 18, over a magnetic read/write head 20, around a second tape guide 22 to a take up spool 24. Head 20 is mounted to a carriage and actuator assembly 26 that positions head 20 over the desired track or tracks on tape 12. Head 20 engages tape 12 as tape 12 moves across the face of head 20 to record data on tape 12 and to read data from tape 12. Tape guides 18 and 22 may be either roller guides or fixed guides. A conventional roller guide is shown in FIGS. 2-5. Referring to FIGS. 2-5, roller guide 28 includes disc shaped flanges 30 and an annular hub 32. Flanges 30 and hub 32 may be machined as a single integral part or as three separate parts bonded together. In either case, flanges 30 function to keep tape 12 at the proper angle as it passes across head 20. If the tape is presented to the head at too great an angle, then the read and write elements in the head may be misaligned to the data tracks. Flanges 30 are also needed to help keep tape 12 properly packed on take up spool 24.
As shown in the detail of FIG. 5, conventional guides have a square corner 34 at the intersection of hub 32 and flange 30. Corner 34 is usually formed at 90xc2x0 or slightly greater than 90xc2x0 (as indicated by angle xcex8 in FIG. 5). If corner 34 is greater than 90xc2x0, then a small flat area 36 is often used to make it easier to measure the spacing between flanges 30 at corner 34. Also, because it is difficult to make a perfectly square corner, a small undercut 35 is often machined into the corner of conventional guides to ensure a flat flange surface is presented to the tape at corner 34.
As the tape is pulled over the guides, a film of air is created between the outside surface 33 of hub 32 and tape 12. This film is often referred to as an air bearing. The air bearing allows the tape to move with low friction very rapidly between flanges 30. Consequently, high frequency tape movement can occur when the edge of the tape bumps abruptly against the flanges 30 at corner 34. The read/write head positioning systems have difficulty following such high frequency tape movement.
U.S. patent application Ser. No. 09/510,834 now abondoned discloses a tape guide in which the corner geometry between the flanges and the hub prevents the tape from abruptly bumping the flange. The tape guide of the ""834 Application, which is incorporated herein by reference in its entirety, includes a hub, a pair of spaced apart parallel flanges extending out from the hub and a corner defining the intersection of the hub and each flange. The corners are configured to apply progressively more force to the edge of the tape as the tape moves around the corner from the hub toward the flange. For example, in one version of the tape guide of the ""834 Application shown in FIG. 9, the corners are rounded. These corner configurations are designed to urge the tape more gently away from the flange at a much lower rate of acceleration. Guiding the tape in this manner allows for smoother movement of the tape which in turn allows the head positioning system to better follow the tape as it wanders back and forth between the guide flanges.
As shown in FIG. 11, the edge of the tape rides on the rounded corner of this new tape guide roller. Since the edge of the tape is somewhat abrasive, it may tend to wear the corners of the roller. This abrasive characteristic is more pronounced with unused tape because the slitting operation used to form the tape leaves the corner of the new tape relatively sharp.
As shown in FIG. 5 and described above, most conventional tape guide rollers have a small undercut or xe2x80x9creliefxe2x80x9d machined into the corner. Conventional rollers are usually made from aluminum with an electroless nickel coating. Aluminum is used because it is easily machined to a good surface finish and it is inexpensive.
Electroless nickel coating is much harder than aluminum and protects the surface against wear and corrosion. The nickel coating provides adequate protection for conventional rollers since the edge of the tape does not ride up on the corner. It has been observed, however, that nickel coating on the new rounded corner rollers of the ""834 Application wears more quickly than is desirable. As the nickel coating wears the rounded corner, the tape may begin to bump more abruptly against an edge or edges worn into the corner.
Accordingly, the present invention is directed to a tape guide like that described in the ""834 Application in which the corner region is coated with a very hard material such as titanium aluminum nitride, tungsten carbide, silicon nitride, chromium nitride or diamond like carbon. Even thin coatings of such materials can be formed to exhibit a surface hardness greater than 10 gigaPascals (GPa). It is expected that coating materials applied to the roller that exhibit a hardness of at least 10 GPa will be sufficient to withstand tape wear in the corners of the roller for tape materials currently used in the manufacture of magnetic data storage tapes.
A tape guide constructed according to the present invention includes a hub, a pair of spaced apart parallel flanges extending out from the hub, and a corner defining the intersection of the hub and each flange. The corners are configured to apply progressively more force to the edge of the tape as the tape moves around the corner from the hub toward the flange. The corners are coated with a material that when applied to the roller exhibits a hardness of at least 10 Gpa. Suitable coating materials include titanium aluminum nitride, tungsten carbide, silicon nitride, chromium nitride or diamond like carbon.